The present invention concerns a dimension-measuring column, in particular a single vertical axis column, as well as a method for entering commands to switch the measure mode in such a column.
The content of Application EP01810258.2, filed on Mar. 14, 2001 with the European Patent Office, is hereby incorporated by reference.
Vertical dimension-measuring columns are frequently used in mechanical workshops or in industry for measuring different vertical coordinates of a work-piece. An example of measuring column 1 is represented diagrammatically in FIG. 1. The shown column comprises a probe tip 12 mounted on a measuring carriage 11 and brought into contact with the piece to be measured 3, as well as a vertical displacement mechanism (not represented) commanded by a crank 13 and making it possible to displace this probe tip vertically along the axis z. The vertical displacement mechanism can be manual or motorized according to the model. A measuring and displaying system 2 allows the vertical position of the probe tip to be determined and displayed on a display. The system 2 also allows the pressing force of the probe tip against the work-piece 3 to be measured. The measuring system uses for example a capacitive, inductive, magneto-resistive or optical sensor comprising for example a scale in the housing 10 and a sensor in the control panel 2.
Usual measuring columns have a housing 10 of a height habitually comprised between 50 centimeters and 2 meters and allow the vertical position of the probe tip 12 to be measured with an accuracy on the order of several microns or less. The piece to be measured 3 is placed close to the measuring column 1 and the probe tip is displaced vertically so as to rest against the portion of the work-piece whose vertical coordinate one wishes to measure. The measuring column 1 can be mounted on an aircushion bearing-plate 14 that facilitates its horizontal displacement. Such measuring columns are described for example in documents U.S. Pat. No. 4,187,612 and U.S. Pat. No. 3,895,356. Such measuring columns are further commercialized by the applicant under the name MICRO-HITE (registered trademark) and TESA-HITE (registered trademark) for example.
Current measuring columns are usually provided with a measuring and displaying system 2 that make it possible to perform measurements according to different modes, for example for displaying either the absolute height of a point, or the difference between two consecutive points of measurement. Control buttons 21 on the measuring system allow the measure mode to be switched. Different examples of useful measure modes are described in the aforementioned patent U.S. Pat. No. 3,895,356.
Measuring columns are also known that allow for example the inner diameter of a hole or the outer diameter of a rod to be measured. For this, it is necessary to measure consecutively the two turn-back points, i.e. the lowest and the highest point of the hole or rod, and to calculate the height difference between these two extremes.
Different systems and methods exist for determining the highest and lowest points of a hole or of a rod by means of a single-axis measuring column 1. For example, devices exist that allow the probe tip to slide horizontally along an axis x perpendicular to the page. By exerting a vertical pressure on the axis z, the probe tip 12 comes to rest of its own against the lowest point, respectively highest point, of a hole. The measurement is accomplished at each of these two points and the difference calculated to determine the diameter and/or center of the hole. These mechanical devices are however costly and influence the overall accuracy of the measuring system. Furthermore, the size of the holes to be measured is limited by the maximal amplitude of the probe tip""s horizontal displacement. Finally, these devices are poorly adapted for measuring outer diameters, for example when the diameter of a rod is to be measured.
Are also known systems capable of determining automatically the turn-back points (extremes) of a hole or rod. For this, it is necessary to enter in the measuring and displaying system 2 a command enabling it to switch into a turn-back point search mode. This command is generally entered by selecting a control button 21 provided on the control panel or a crank (not represented) close to the probe tip 12. The piece to be measured 3 or the measuring column 1 is then displaced horizontally, by maintaining the holding pressure between the probe tip and the work-piece, so as to scan the area close to the highest or lowest point by overshooting at least once the turn-back point. An extreme-computing algorithm determines the vertical coordinate of the turn-back point; an acoustical and/or optical signal confirms that the point""s vertical coordinate has been calculated. The use must then deselect the automatic turn-back point search mode, then displace the probe tip to perform a new measurement, for example to determine the position of the other extreme of the hole or rod in order to calculate its diameter.
These systems have the inconvenience of requiring an important number of handling operations, which renders their use less intuitive. Furthermore, it is necessary to let go of the piece to be measured 3 or the crank 13 for controlling the vertical position of the probe tip in order to switch to the turn-back point search mode. Furthermore, the presence of control buttons 21 whose only function is to switch the measure mode increases the cost of the device.
It is thus an aim of the present invention to propose a method for entering commands to switch the measure mode in a vertical dimension-measuring column that avoids these inconveniences, as well as a measuring column that is improved and easier to use than the measuring columns of the prior art.
According to the invention, these aims are achieved by means of a method and of a measuring column having the characteristics of the corresponding independent claims, variants of preferred embodiments being moreover described in the dependent claims.
In particular, these aims are achieved by means of a method enabling a command to switch the measure mode to be entered in a dimension-measuring column, wherein this mode-switch command is entered by only making use of the position of the probe tip.
This method has the advantage that the mode switch is effected by making use of the position of the probe tip in a particular manner that is different from the manner used for measuring a position and that allows the mode switch to be indicated. It is thus not necessary to let go of the piece to be measured 3 or the height command crank 3 in order to switch the measure mode. Furthermore, no additional button 21 is required.
Preferably, the switch of measure mode is entered by means of deliberate handling operations of the device for controlling the probe tip""s position and is confirmed by an aural and/or visual signal. This ensures that the risk can be prevented of the system switching measure mode spontaneously or independently of the user""s will.
The invention is based on the observation that the attention of the measuring column user is concentrated at each moment on the position and the trajectory of the probe tip 12. Tests with users have shown that it is more rapid and more intuitive to enter commands to switch the measure mode by acting on this position or trajectory rather than by operating the control panel 2 of the measuring column.
According to a preferred characteristic of the invention, these aims are further achieved by means of a method according to which the command to switch the measure mode is entered by pressing the probe tip against the piece to be measured during a time interval greater than a predetermined value.
This characteristic has the advantage of permitting a very quick and intuitive mode switch: as soon as the probe tip is pressed against the work-piece for a duration greater than the predetermined threshold value, the measuring and displaying system switches measure mode. This switch can be confirmed by an aural and/or visual signal.
According to another preferred characteristic of the invention, the measuring column allows the pressing force of the probe tip against the work-piece to be measured. The command to switch the measure mode is preferably also entered by acting on this pressing force, for example by maintaining the pressing force constant during a predetermined time interval.
Preferably, the switch of measure mode is entered by means of deliberate handling operations of the device for controlling the probe tip""s position and is confirmed by an aural and/or visual signal. This ensures that the risk can be prevented of the system switching measure mode spontaneously or independently of the user""s will.